Earphone



Aug. 3, 1943.

R. W. CARLISLE ET AL EARPHONE Filed May l1 1940 Y, ff-

2 Sheats-Shee't 1 3 lNvl-:NoR 3mi). @rfi/:band (1. 'BY 5 han@ duATTORNEY Aug. 3, 1943. R. w. CARLISLE ET AL EARPHONE Filed May l1, 1940ATTORNEY Patented Aug. 3, 1943 EARPHONE Richard W. Carlisle, Elmsford,and Alfred J.

Mastropole, New York, N. Y., assignors to Sonotone Corporation,Elmsford, N. Y.,

tion of New York Application May 11, 1940, Serial No. 334,678

8 Claims.

This invention relates to earphones, and particularly to midget sizeearphones of the type used by deafened persons, small enough to be wornand held within the ear of the user.

Among the objects of the invention is an improved midget earphonecombining within an extremely small structure various features whichsimplify its manufacture, assembly and accurate adjustment in aneiil'cient operating condition essential for producing with such smallunit the relatively large volume of relatively high quality outputrequired from a satisfactory hearing aid; and improved methods andarrangements for selectively controlling and adjusting the outputcharacteristics of such earphone so as to t best the needs of the user.

The foregoing and other objects of the invention will be best understoodfrom the following description of exemplications thereof, referencebeing had to the accompanying drawings in which Fig. 1 is a verticalcross-sectional view through a midget earphone illustrating one form of'the invention as it is held Within the ear of the user;

Fig. 2 is an elevational view of the receiver without its cap;

Fig. 3 is an exploded view of the principal elements of the earphone;

Fig. 4 is a perspective view of the assembled elements of the magneticdriving structure of the earphone;

Figs. 5 and 6 are cross-sectional views along line 5 6 of Fig. 7 of twointerchangeable tone control units for the earphone;

Fig. 7 is a top view of the tone control unit;

Fig. 8 is a cross-sectional view along line 8 8 of Fig. 7 of a similarinterchangeable control element;

' Fig. 9 is a sectional view along line 9-9 of Fig.`

10 of an arrangement foi` locking the earphone cap in its adjustedposition;

Figs. 10 and 11 are elevational and sectional views, respectively, ofthe locking arrangement of Fig. 9;

Fig. 12 is a view similar to Fig. 9 of a modified form of lockingarrangement;

Fig. 13 is an exterior view of another form of an earphone of theinvention and a horizontal section of the adjacent portions of the earin which it is held;

Fig. 14 is a horizontalsectional view of the earphone of Fig. 13;

Fig. l5 is an exploded view of the cap elements of Fig. 14; and

Figs. 16 and 17 are views Vof two interchangeable tone control units forthe earphone of Fig. 13.

Most of the deafened are very sensitive and seek to conceal theirhearing impairment. Accordingly, a satisfactory hearing aid device forsupplying the deafened person with the sound energy required to overcomehis handicap must be suitable for comfortable and inconspicuous Wear andsimple and foolproof in operation so as to free the user from physicalas well as mental strains. All the elements of the device must not onlybe small and light in Weight, but must be able to respond at highefficiency to all important speech frequencies and they must operatesatisfactorily under all conditions of use,7 without special attentionand frequent reconditioning.

Many efforts have been made in the past to make the hearing aid midgetearphones worn in the ear of the user as small, as comfortable and aseiiicient as possible so as to meet the foregoing requirements. f

It was also long known that the hearing deficiencies of differentindividuals vary over the range of audible'sound frequencies, and thatit is very important to make it possible to selectively control thefrequency response of earphones in accordance with the individual needsof each user.

The earphone of the invention is of much simpler construction thansimilar prior earphones, and embodies various desirable novel featureswhich make it possible to more accurately manufacture, assemble andadjust such earphone, and to reduce its overall size Without decreasingits output and quality.V

The invention also provides novel methods and arrangements forselectively controlling the frequency characteristics of the earphoneoutput so that lit fits best the needs of the user.

The various features of the invention will be more readily understoodfrom the description of an exemplication thereof in the form of themidget earphone shown in Figs. 1 to 4 which is designed to serve as apart of a hearing aid in which the receiver winding may be traversed bya D. C. current component in addition to the speech frequency currentoscillations used for its operation.

The earphone is of the electromagnetic type and has an electromagneticdriving structure formed of an outer pole plate 2l to which is secured aparallel inner pole plate 22 having an angularly bent pole arm 23projecting into the opening 24 of the pole plate 2 I, and a permanentmagnet block 25 is held suitably clamped between the parallel portionsof the pole plates 2|, 22, as by three screws 26 extending throughnotches provided in the periphery of the block 25.

'I'he permanent magnet block 25 has at parallel walls against which thetwo parallel pole plates 2|, 22 are clamped and is made ofgood-qualitypermanently-magnetizable material. Permanent magnet blocksmade of powdered 'Alnico material, which is sintered in the moldedshapeshown in the drawings, are used in the practical construction ofsuch earphones. On the pole arm 23 of the pole plate 22 is mounted theactuating-winding coil 21 of the electromagnetic driving structure.

The hole 24 of the outer pole plate 2l is made large enough to enablethe insertion of the coil 21 into its place on the pole arm 23 after theassemby of the magnetic driving structure shown in Fig. 4 has beencompleted. This is important in the manufacture of such midget earphonesbecause it makes it possible to sand oi or grind to an even fiat alignedsurface level the pole face of the pole arm 23 and the adjacent face ofthe outer pole plate 2|,- and to blow out the chips caused -by thisoperation before the coil is inserted. In addition, coils may be easilyexchanged and replaced without disturbing the aligned magnetic drivingstructure.

The flat surface of the outer pole plate 2| serves as an aligningsupport for the vibratory diaphragm structure 3|. The diaphragmstructure 3| is formed of a flat spring metal plate to which is secured,as by soldering, a fiat central magnetic armature portion 32 and a flatperipheral stiifening ring 33, which are so arranged that by aligningthe periphery of the diaphragm 3| on the outer pole plate 2| thepoleface of the armature 32 will be symmetrically aligned parallel andopposite to the pole faces of the pole arm 23 and the pole plate 2| andwill enable accurate adjustment of the magnetic gap between thepolefaces of the vibrating structure so formed. As shown in Fig. 1, thearmature 32 bridges the magnetic path between the pole faces of the polearm 23 and the aligned adjacent portion of the pole plate 2|, whichk arespaced from the parallel pole face of the armature 32 by accuratelyadjusted gaps.

The aligning member formed by the outer pole plate 2| serves also as theclamping junction for clamping the armature diaphragm 3| in itsaccurately spaced and aligned position opposite the electromagneticdriving structure. As shown, the outer plate 2| has a threaded circularperiphery which is engaged by an inwardly threaded cylindrical clampingring 34 of the cap plate 35 so as to clamp the periphery of thediaphragm 3| in its aligned position and provide between its exteriorsurface and the cap plate 35 an acoustic chamber. The cap plate 35 has aprojecting knob or tip 38 forming a sound outlet passage to theexterior. The-cap 35 and its clamping ring 34 may -be made of one piece,or, as shown, `of two parts so as to make it possible to adjust theangular position of the cap plate 35. The armature is accurately spacedby a spacer ring 31 of the required thickness.

A spring ring 38 transversely bent into a wavy shape is clamped betweenthe rimof .the cover plate 35 and the rim of the armature diaphragm 3|so as to hold al1 operating parts clamped in their adjusted position.

In the earphone receiver assembly described above. the pole plate 2l.which. as shown is a very solid rigid part, serves thus asf an aligningmember which makes it easy to align "on its opposite sides the elementsof the electromagnetic vibrating system and the acoustic chamber, and tomaintain with a minimum of effort and care the accurate'magnetic gapspacing and eicient 4operating conditions essential for producing with atiny unit tting within the ear of the person the relatively large soundoutput of good quality that is required from a satisfactory hearing aidearphone.

The earphone has also a casing shell member 4| which, in distinctionfrom prior earphone designs, does not perform any functions, except toserve as enclosure for the parts of the magnetic structure mounted onthe inner side of the aligning pole plate 2|, the casing being heldclamped thereto by i'lat head screws 42 held in inwardly threadedbushings 43 of the casing 4|.

This arrangement makes it possible to mold the casing shell 4| of arelatively cheap synthetic resin material. Since the casing shell 4|isnot used as a reference element for aligning the various parts of thevibrating system and the acoustic chamber, inaccuracies in molding orWarpage will not in any way aiect the accurate adjustment of theoperating elements of the earphone.

The winding ends of the actuating coil 21 are connected to two terminalbushings 44 which extend through a slanted side wall portion 45 of thecasing shell 4| at an angle to the generally fiat parallel main walls ofthe earphone structure. so that when the cord plugs 46 of the connectingcord are inserted in the terminal bushing 44, the outwardly projectingplug portions shall not interfere with the insertion of the earphoneinto the space within the outer ear.

By mounting all the elements of the earphone, which cooperate intranslating the electric oscillations delivered to the earphone intosound energy delivered to the ear of the user, on the opposite sides ofa at solid aligning plate, all operating parts'may be made of simpleshape and easily machined to accurate dimensions, thereby enabling easyassembly and accurate adjustment of all parts in their eicient operatingpositions.

The aligning plate 2| which is used as a common level for all' operatingparts, serves also as the support of the housing shell 4| which is sosecured thereto that warpage or any inaccuracies in its dimensionscannot affect the adjustment of the operating parts.

As shown in the drawings, the sound outlet knob 36 projecting from thecover plate 35 is offset from the center and is shaped to clamp theearphone toan ear tip 5u molded to i'lt the outer'ear of the user. Theear tip 50 has a cavity 5| for receivingthe outlet knob 36 of theearphone which is held clamped therein by a snap fastener ring 52retained in a collar insert embedded in the molded body of the ear tip50. A sound passage 53 extending through the projecting portion of theear tip registers with and ts into the mouth of the ear canal so thatthe sound generated in the acoustic chamber of the ear phone will betransmitted through the knob passage 36 and the ear tip passage 53 tothe ear canal of the user.

In the drawings is shown an ear tip 50 molded to t a very small size earand, as shown, the diameter of the earphone is confined within thecircumference of the at ear tip surface facing it.

The size of such midget earphones presents netic path betweenthe thefollowing problem: Deafened persons are very anxious that the earphonepossible and that it should not be noticeable. In order to meet theserequirements, the diameter of the earphone must be kept down if possibleso that it should fit within the lobe of avery small ear of a youngperson. In addition, it is desirable that the earphone should lie asflush within the lobe of the ear as feasible. turn requires that itshould not be thicker than about of an,r inch.

'I'he receiver of the invention meets these requirements. Its outerdiameter is only .7 of an inch. As shown in the drawings, the midgetearphone is thicker than thecoil principally by the thickness of theinner pole'plate 22 and the amature 32. Accordingly, the thickness ofthe midget cannot be substantially reduced without reducing the size ofthe coil.

Since, as explained hereinabove, the earphone shown in the drawings isdesigned for use in hearing aids which send a D. C. current componentthrough the earphone coil 2l, a considerable heat is evolved in the coiland the coil of the dimensions shown is just about adequate to take careof such heating effect.-

The midget earphones of the invention of the type shown in the drawingsmay be made considerably thinner if they are designedl for use only inhearing aids which do not send a direct current component through thereceiver coil 2l.

The thickness of a receiver designed for such use could be reduced by atleast 11g of an inch so that its overall thickness would be 11g of aninch less than that shown.

By making the permanent magnet block with notches, it is automaticallypositioned in its proper place between the pole plates 2|, 22 and theshanks of their clamping screws 26 when assembled. In addition, thisarrangement provides a large cross-sectional area for the magtwo poleplates having a suiilciently low magnetic reluctance to assure eiiicientoperation of the receiver without necessitating special magnetic shuntpaths for thealternating magnetic flux.

The coercive magnetic force of the permanent magnetic material used inthe earphone is large enough to supply the required permanent magnetflux if its total thickness or its effective length between the poleplates is made as little as 11.; of

an inch. Such construction would require a very short magnetic air gapof less than three thousandths of an inch between the armature and thecore structure. If it is desired to operate such receivers with a largerair gap of the order of three to iive thousandths of an inch, it isbetter to use a permanent magnet block 25 having an eiective length orthickness of 1/8 of an inch between the pole plates 2|, 22.

The design features of the earphone described above eliminate disturbingeii'ects of temperature changes on the adjustment of its cooperatingelements that are otherwise encountered in such earphones. The responseof the earphones may be regulated by using armature diaphragm structuresof different resonant frequencies'.

Thus, an earphone shown in the drawings having an armature 32approximately .030 inch thick will resonate around 1100 cycles; onehaving an armature approximately .022 inch thick will resonate around1500 cycles; and one having an armature approximately .015 inch willresonate around 1800 cycles.

Midget receivers operating with such resonant This in shall be as smallas n netizin'g the permanent magnet 25 less strongly.

. This effect is desirable 'coupling to the outer end Where an increasein low frequency output is desired, the permanent magnet 25 ismagnetized to less than full value. Ii it is desired to damp themechanical resonance oi' the armature diaphragm and to extend the highfrequencyrange, the thickness of the acoustic cavity between thearmature diaphragm 3| and the cap plate 35 should be kept down toapproximately .012 to .015 inch. In some cases, additional-damping maybe provided by placing a piece of cotton inthe cavity 5| of the ear tip50 in order to attenuate the resonance peaks, or to adjust the output onhigh signals to a critical level that will not be uncomfortable to theuser.

Because of its acoustic propagation characteristics, the air in the'knoboutlet passage 36 acts as an inertance and has the effect of slightlyattenuating frequencies above about 4000 cycles. since the frequency'band above 4000 cycles contains more noise than useful signals. If theacoustic cavity between the diaphragm 3| and the cap 35 is made toolarge, the air therein acts as a compliance which accentuates'theeffects of the inert-ance of the knob outlet passage and increases theattenuation of the high frequencies.

If the audiometric measurement of the user indicates that the diminutionof the high frequency output is desirable, or'if the user isparticularly sensitive to distortion in the high frequency range, it isdesirable to controlv the attenuation of the high frequency output. Asshown in Figs. 1 to 3, such control of the high frequency output may besupplied by attaching to the outer end of the knob outlet duct 36 anoutlet duct extension in the form of a washerlike plug member 55provided with a relatively elongated hole 56 of small cross section.

As shown in Figs. 5 to 8, the tone control washer 55 is made very iiatso as to occupy only a portion of the cavity 5| of the ear tip 50. 'Ihehole 56 is arranged to extend diagonally through the flat body of thewasher 55 so that its inertance effect is increased, and to assure thatthe outlet end of `the hole 56 opening into the shall not be clogged bya piece of cotton .placed therein. Such acoustic control plug 55 havinga hole about .020 in diameter will reduce the output by about six deci-'bels at 4000 cycles and will hardly have any effect at 1000 cycles andbelow.

By using a set of acoustic or duct extensions 55, designed fordetachable of the outlet knob of the acoustic chamber of the earphone,each having a hole 56 of diiTerent diameter, as shown in Figs. 5 and 6,the frequency `characteristics or the tone of the output of a midgetearphone may be adjusted in accordance with the needs of the user.VSimple interchangeable attachment is made possible by providing eachduct extension 55 with a spring projection 51 formed of two doubled-overthin wires anchored in a hole 58 of the washer, the free ends of thesprings being bent outwardly to engage the inner edge of the outlet duct36 and hold it clamped therein. As shown in Fig. 1, thesound outlet duct36 of the control washer plugs cover wall 35 has at its outer end anoutwardly facing non-planar, tapered, seating surface intertting withthe complementary seating surface formed on the inward end of the ductextension washer 55; and the surface of the inner end of the outlet duct36 is slightly tapered to Areceive the ends of the retainer springs51ofthe duct extensions 55, without increasing the height of the acousticchamber of the earphone.

Instead of employing a set of duct extensions 55, of different acousticinertance characteristics for selectively fitting the outputcharacteristics of the earphone in accordance with the needs of theuser, the control washer may be made with a very small hole 56 having aninertance effect required in extreme cases, which is then adjusted inaccordance with the needs of the user, by successively enlarging it, bya set of graduated reamers or drills.

Alternatively, the outlet passage 53 of the molded ear tipv 50 may beused for adjustably `controlling the frequency or tone of the earphoneoutput. To this end, the vear tip passage 53 is provided with an innerportion 54 forming a hole of reduced cross section which is soproportioned as to have an acousticinertance effect required in extremecases. 'I'he tone of the earis mounted a locking screw 63, the head ofwhich is located and arranged to engage the inwardly phone output isthen adjusted in accordance with the needs of different users bysuccessively enlarging the narrow hole 54, for instance, by a set ofgraduated reamers or drills. As another alternative, the portion of theear tip 50 surrounding its narrow tone control hole 54 may be made inthe form of an interchangeably mounted insert plug, of metal, forinstance, so as to enable adjustment of the tone in accordance with theneeds of the user, by inserting into the ear tip passage 53 one of a setof insert plugs having tone control holes 54 of diiferent graduatedcross sections.

The earphones of the type shown may be used either in hearing aids inwhich its Aactuating coil is traversed by a direct-current component, orin which the coil is traversed only by alternating current. Becauseofthe small size of the earphone, maintenance of the gap spacing betweenthe armature and adjacent pole faces in' a critically adjustedpositionis ofcontrolling importance. In some cases, it may be-.veryimportant to maintain thel acoustic cavityl inbetween the diaphragmandthe 'cap critically adjusted. The magnetic gap may be criticallyadjusted by placing a. 'sp-ring washer, such as.v spring washer 38,between the diaphragm 3| and the pole plate 2|, and one or more thinflat washers, such as washer 31, of the predetermined desired thicknessbetween the cap wall 35 and the diaphragm 3| of,

the acoustic chamber. Thereupon, the cap rim 34 is turned against thepressure of the spring washer until the gap 'is adjusted inthe operat-`ing position in which it meets best the needs of the user. If criticaladjustment of the acoustic cavity is desired, the'spring washer isplaced betweenvthe vdiaphragm vand 'the capvwall, while one or more thinwashers of predetermined thickness are placed between the pole plate 2|and the diaphragm 3|, andthe cap rimy 34 is turned to critically adjust.the acoustic cavity.

In order to assure that the earphone remains in the critically adjustedposition, :it is provided with an arrangement for locking it in theadjusted position. l I

As shown in Figs. 9 to 11, the side wall of the casing 4| is providedwith an vinward protrusion 6| having an inwardly threaded hole 62 inwhich facing edge portion of the clamping collar 34 of the earphone cap35. The cap collar 34 may be locked in the adjusted position of the capby turning the locking screw 63 outwardly until it engages and clampsthe cap collar or rim 34 against rotation. By turning the locking screw63 inwardly, the cap collar 34 is released from its locking engagement,whereupon it may be turned to adjust either the gap or the acousticchamber, whereupon it is again locked in the adjusted position byturning the locking screw 63 outwardly. The head of the locking screw 63is provided with cross grooves to permit its being turned by a screwdriver and its outer surface is slightly curved to facilitate itslocking engagement with the inner edge of the cap rim 34.

As shown in Fig. 9, a lirm anchorage of the `adjusting-screw within thethin wall of the casing metallic projection 66 may be formed either aspart of the pole plate 2| or may be suitably secured thereto, as byfusing or welding.

Instead of lsupporting the earphonel on a molded ear tip fitting andheld within the outer ear, such midget earphones may be held directlyWithin the cavity of the ear between the tragus and the anti-tragus, inthe way shown in Fig. 13.

As shown in Figs. 13 to 15, in order to provide 1 a tight sound passagebetween the acoustic chamber of the earphone 'and the mouth of the earcanal, the earphone is provided with a receiver cap 1| having anangularly projecting sound outlet duct portion 13 to which is connectedby a self-adjustable junction a small ear ltip duct .14' fitting andengaging the entrance portion of the ear canal 15.

In the form shown, the earphone cap 1| has a molded protruding portion12in which isv held, as by threads, the outlet duct 13, which is of metaland forms a swivel stud having a ballshaped end portion 16 fitting intoa spherical seating surface of a swivel socket ring 11 embedded in themolded body of theear tip duct 14.

As shown, the swivel socket ring 11 of the ear tip duct 14 is providedwith a snap fastener ring so that when it is inserted on the swivel stud16 it is retained in a self-adjustable position on its ball, so as tocomplete a substantially tight sound passage from the earphone outletduct 13 through the ear tip duct 14 into the ear canal 15..

By providing a plurality of ear tip ducts 14 of different exteriordimensions, in the way shown in Figs. 16n and 17, but all designed forinterchangeable self-adjustable clamping engagement with the swivel endof the earphone outlet duct 13, the same earphone may be fitted to earsof different sizes without requiring laborious and expensive molded eartips of the type shown in Fig. 1, while assuring substantially the samedegree of acoustic coupling between the acoustic l cavity of theearphone and the ear canal. By

providing sets of such interchangeably detachable swivel-type ear tipducts 14 having sound passages 18 of different cross sections, they lmayalso be used instead of the washers 55 for controlling the tone or thefrequency response of the earphone.

Alternatively, all ear tip ducts 14 may be provided with a passage ofsuch small cross section as to provide for the most extreme casesrequiring such type of tone control. The tone of the earphone output isthen adjusted in accordance with the needs of different users byenlarging the passage 18 of the ear tip duct 14, for instance, by agraduated set of drills or reamers.

'I'he exemplifications of the novel features of the invention describedabove which simplify and at the same time make possible much moreaccurate manufacture, assembly and critical ad- .iustment of midgetearphones for hearing aids and the like, and to modify their outputcharacteristics so as to iit best the needs of the user, will suggest tothose skilled in the art many other modifications thereof. It isaccordingly desired that the appended claims be construed broadly andthat they shall not be limited to the specic details shown and describedin connection with the exemplications thereof.

We claim:

1. In an earphone designed to be small enough for carrying in the ear ofthe user, an electromagnetic vibratory structure comprising asubstantially rigid plate-like aligning member having a circularperiphery and an opening in the interior thereof; a magnetic corestructure clamped in a predetermined aligned position to one side ofsaid aligning member and having a pole projection extending into saidopening; a vibratory diaphragm .having a periphery supported in apredeterminedly aligned position by the periphery of the other side ofsaid aligning member, said diaphragm having` a magnetic ar` matureportion driven by said core structure and held in a vibratory conditionopposite said pole projection at a predetermined small gap spacingtherefrom; and cap means having a cap wall including a capv outlet Vductoverlying said diaphragm to confine therebetween an acoustic VAchamber,and a cap rim held in detachable interlocking engagement with theperiphery of said aligning member and holding clamped thereto saiddiaphragm and said cap wall; and a casing portion held in a position inwhich it encloses said core structure and is prevented from affectingthe adjusted relation of the elements of the magnetic structure securedto said aligning member; and locking means including a locking screwmounted in a part of the earphone structure surrounding the poleprojection and having an outer surface shaped so that upon turning it onits threads it will interlockingly engage or release an interior edgeportion of said cap rim.

2. In an earphone designed to besmall enough for carrying in the ear ofthe user, an electromagnetic vibrating structure comprising asubstantially rigid plate-like aligning member hav'- ing a circularperiphery and an opening in the interior thereof; al magnetic corestructure clamped ina predetermined aligned position to4 one side "ofsaid aligningmember and having a y pole projection extending into saidopening; a vibratory diaphragm having a periphery `supported in apredeterminedly aligned position by the periphery of the other side ofsaid aligning member, said diaphragm having a magnetic armature portiondriven by said core structure and held in a vibratory conditionoppositesaid pole projection ata predetermined small gap spacing therefrom; andcap meanshaving a cap wall including a, cap outlet duct overlying saiddiaphragm to confine therebetween an acoustic chamber, and a cap rimheld in detachable inter- 5 locking engagement with the periphery ofsaid aligning member and holding clampedV thereto said diaphragm andsaid cap wall; anda casing portion held in a position in which itencloses said core structure and is prevented from affectingv theadjusted relation of the elements of the magnetic structure secured tosaid aligning member; and locking means includlnga locking screw mountedin a part of the earphone structure surrounding the pole projection andhaving an outer surface shaped sov that upon turning it on its threadsit will interlockingly engage or release an interior edge portion ofsaid cap rim projecting beyond the periphery of said aligning member.

3. In an earphone` designed to be small enough for carrying in the earof the user, an electroacoustic transducer structure including a casingportion having a rear Wall and a side wall enclosing a part of saidtransducer structure and an aligning portion having a, circular aligningperiphery; 'a vibratory diaphragm having a periphery supported in apredeterminedly aligned position relatively to said aligning periphery;cap means having a cap wall including a cap outlet duct overlying saiddiaphragm to confine therebetween an acoustic chamber, and a cap rimdetachably engaging and overlapping said aligning periphery and holdingclamped thereto said diaphragm and said cap wall; and locking meansincluding a locking screw mounted in a part of the transducer structuresurrounded. by said casing portion and having an outer surface shaped sothat upon turning it on its threads it will interlockinglyengage orrelease an interior edge portion of said cap rim.

4. In an earphone designed to be small enough for carrying in the ear ofthe user, an electroacoustic transducer structure including a casingportion having a rear Wall and a side wall enclosing a part of saidtransducer structure and an aligning portion having a circular aligningperiphery; a vibratory diaphragm having a periphery supported in apredeterminedly aligned position relatively to said aligning periphery;cap means having a cap wall including a cap outlet duct overlying saiddiaphragm to confine therebetween an acoustic chamber, and a cap rimdetachably engaging and overlapping said aligning periphery and holdingclamped thereto said diaphragm and said cap wall; and locking meansincluding a locking screw mounted in a part of the transducer structuresurrounded by said casing portion and having an outer surface shaped sothat upon turning it on its threads it will in- `terlockingly engage orrelease an interior edge portion of said cap rim,` said locking screwbeing held in a wall portion of said casing portion.

5. In an arrangement for fitting la hearing aid including an earphonesmall enough for. carrying `in the ear of the user so as to compensatefor his individual hearing impairment; said earphone comprising anelectroacoustic transducer structure including a casing portionenclosing a part of said transducer structure and an aligning portionhaving a circular aligning periphery; a vibratory diaphragm having aperiphery supported in a predeterminedly aligned position re1- ativelyto said aligning periphery; a cap structure having a cap wall overlyingsaid diaphragm to conne therebetween an acoustic chamber, and

a cap rim detachably engaging and overlapping said aligning peripheryand holding clamped thereto said diaphragm and said cap wall; said capwall having integrally formed thereon an outwardly projecting soundoutlet duct having at outwardly in the general direction of the ductpassage; and a set of a plurality of outlet duct extensions, each ductextension having a complementary seating surface sealingly interttingwith the outwardly facing seating surface of said duct portion andjunction means for detachably joining it to the end of said cap outletduct, and

different duct extensions of said set having a different internal crosssection for enabling controllable adjustmentof the frequencycharacteristlcs of the earphone output in accordance with the needs ofthe user; each of said duct extensions being designed to form part of ahollow ear tip member shaped and arranged to fit into the ear canal andto provide a substantially air-tight sound passage from said acousticchamber to ported in a predeterminedly aligned position relatively tosaid aligning periphery; a. cap structure having a cap wall overlyingsaid diaphragm toconiine therebetween an acoustic chamber, and a cap rimdetachably engaging and overlapping said aligning periphery and holdingclamped thereto said diaphragm and said cap wall; said cap wall havingintegrally formed thereon an outwardly projecting sound outlet ducthaving at its Outer end a non-planar seating surface facing outwardly inthe general direction of the duct passage; and an outlet duct extensionhaving a complementary seating surface sealingly interltting with theoutwardly facing -seating surface of said duct portion and junctionmeans for detachably joining it to the end of said cap outlet duct, saidduct extension being designed to form part of a hollow ear tip membershaped and arranged to t into the ear canal and to lprovide asubstantially air-tight sound passage from said acoustic chamber to theear canal.

7. In an arrangement for fitting a hearing aid including an earphonesmall enough for carrying in the ear of the user so as to compensate forhis individual hearing impairment: said earphone comprising anelectroacoustic transducer structure including a casing portionenclosing a part of said transducer structure and an aligning portionhaving a circular aligning periphery; a vibratory diaphragm having aperiphery supported in a predeterminedly aligned position relatively tosaid aligning periphery; a cap structure having a cap wall overlyingsaid diaphragm to conne therebetween an acoustic chamber, and a cap rimdetachably engaging and overlapping said aligning periphery and holdingclamped f its outer end a non-planar seating surface facing thereto saiddiaphragm and said cap wall; said cap wall having integrally formed`thereon an outwardly projecting sound outlet duct having at* its outerend a non-planar seating surface facing outwardly in the generaldirection of the duct passage; and a set of a plurality of outlet ductextensions, each duct extension having a complementary seating surfacesealingly intertting with the outwardly facing seating surface of saidduct portion and junction means for detachably joining it to the end ofsaid cap outlet duct, and diierent duct extensions of said set having adifferent internal cross section for enabling controllable adjustment ofthe frequency characteristlcs of the earphone output in accordance withthe needs of the user; each of said duct extensions being designed toform part of a hollow ear tip member shaped and arranged to fit into theear canal and to provide a substantially airtight sound passage fromsaid acoustic chamber to the ear canal; said junction means and theseating surfaces of said sound outlet duct and said duct extensionsbeing so shaped and arranged as to constitute a self-aligning universaljoint junction enabling self-aligning adjustment of each of the outletduct extensions in different angular positions relatively to the soundoutlet duct.

8. In an arrangement for fitting a hearing aid including an earphonesmall enough for carrying in the ea'r of the user so as to compensatefor his individual hearing impairment: said earphone comprising anelectroacoustictransducer structure including a casing portion enclosinga part of said transducer structure and an aligning portion having acircular aligning periphery; a vibratory diaphragm having a peripherysupported in a predeterminedly aligned position relatively to saidaligning periphery; a cap structure having a cap wall overlying saiddiaphragm to confine therebetween an acoustic chamber, and a cap rimdetachably engaging and overlapping said aligning periphery and holdingclamped thereto said diaphragm and said cap wall; said cap wall havingintegrally formed thereon an outwardly projecting sound outlet ducthaving at its Outer end a non-planar seating surface facing outwardly inthe general direction of the duct passage; and an outlet duct extensionhaving av complementary seating surface sealingly interitting with theoutwardly facing seating surface of said duct portion and junction meansfor detachably joining it to the end of s aid cap outlet duct, said ductextension being designed to form part of a hollow ear tip member shapedand arranged to fit into the ear canal and to provide a substantiallyair-tight sound passage from said acoustic chamber to the ear canal;said junction means and the seating surfaces of said sound outlet ductand said duct extension being so shaped and arranged as to constitute aselfaligning universal joint junction enabling selfaligning adjustmentof said outlet duct extension in different angularpositions relativelyto the sound outlet duct.

RICHARD W. CARLISLE. ALFRED J. MASTROPOLE

